An area cathode of the present invention is particularly although not exclusively useful in display applications, especially flat panel display applications. Such applications include television receivers and visual display units for computers, especially although not exclusively portable computers, personal organisers, communications equipment, and the like.
All flat panel CRT technologies require an area cathode, that is a uniform planar source of electrons the same area as the display. There have been many designs developed over the years, based on technologies such as Field Emission Devices (FEDs), Metal-Insulator-Metal devices (MIMs) and the like. Probably the most successful types have been the virtual thermionic cathode from Source Technology, disclosed in European Patent Application 0 213 839, and the secondary emission channel hopping cathode developed by Philips for their Zeus display. All current designs, however, suffer from significant disadvantages of one sort or another. In particular the virtual thermionic type has high power and hence a major heat dissipation problem, and the channel hopping type has high and non uniform channel extraction voltages.
U.S. Pat. No. 5,227,691 discloses a flat tube display apparatus in which a row of many electron beam generators is arranged transversely in a thin flat vacuum tube body to generate a number of beams in parallel with each other which travel in parallel with an image screen and in which the electron beam generators are arranged to deflect the beams toward the image screen at a predetermined position. The beams are guided without being widely diverged due to the provision of a number of side walls arranged in parallel with each other to confine the beams and due to the provision of alternately strong and weak magnetic fields along the side walls forming periodic magnetic lenses. The electron beams are deflected electrostatically or using a magnetic field towards an electron beam multiplier and a phosphor screen.
It would be desirable to produce an area cathode that has:
1. An electron source based on known materials; PA0 2. Generation of electrons at a low eV (hence low extraction voltages); PA0 3. A narrow eV spread (hence low beam spreading); PA0 4. A high degree of uniformity; PA0 5. Low power and heat; PA0 6. Isolation from external electric and magnetic fields; PA0 7. Protection of the electron source from ion bombardment; and PA0 8. Mechanical simplicity leading to low cost.